The present invention relates to a power train for an amphibious vehicle and in particular, though not exclusively, to a power train for driving the rear wheels and the marine propulsion means of an amphibious vehicle. The present invention also relates to an amphibious vehicle.
In an amphibious vehicle it is advantageous to use a power train in which the prime mover, which will typically be an engine, and transmission are positioned towards the rear of the vehicle for driving the rear wheels of the vehicle. The weight of the power train is therefore positioned towards the back of the vehicle, which is necessary for good vehicle performance when the vehicle is in marine mode and in particular when the vehicle is planing. Furthermore, the rearward position of the power train maximises the space available towards the front of the vehicle for the passenger compartment.
It has been proposed in FIG. 3 of our co-pending European patent application No. EP 1 174 300 to provide a mid-engined vehicle having a transverse power train, with a power take-off for driving a water jet unit. However, as in other known amphibious vehicle arrangements, the drive shaft of the water jet unit is in line with the vehicle axis, and the axis of rotation of the power take-off is perpendicular to the vehicle axis. Consequently, it is necessary to turn the axis of drive from the power take-off through 90xc2x0 by means of a pair of bevel gears.
This arrangement has the disadvantages of reducing the power output of the power take-off to the water jet unit due to frictional losses in the bevel gears, and of being costly to produce. The bevel gears also occupy space in an area of the vehicle where space is at a premium, and require housing in a specially designed casing.
It is an object of the invention to provide a power train for an amphibious vehicle in which the above mentioned disadvantages are reduced or substantially obviated. It is a further object of the invention to provide an amphibious vehicle having such a power train.
According to a first aspect of the present invention, there is provided a power train for an amphibious vehicle, the power train comprising a prime mover, a transmission and a power take-off adapted to provide drive to an impeller of a marine propulsion means, in which a rotational axis of the power take-off and the rotational axis of the impeller are both substantially perpendicular to the longitudinal axis of the vehicle.
Preferably, the power take-off comprises a driving sprocket which drives a driven sprocket by means of a belt or chain. Alternatively, the power take-off may comprise a series of two or more gears.
Preferably, a decoupler is provided to selectively couple and decouple drive from the power take-off to the impeller of the marine propulsion means.
Preferably, the marine propulsion means is a centrifugal pump.
Advantageously, the prime mover and transmission are adapted to be mounted towards the rear of an amphibious vehicle so as to provide drive to a pair of rear wheels of the vehicle.
Preferably, the prime mover is an engine. Alternatively, the prime mover may be an electric motor which may be powered by a fuel cell.
In accordance with a second aspect of the invention, there is provided an amphibious vehicle comprising a power train in accordance with the first aspect of the invention.